Water deficit is one of the most widespread environmental stresses limiting plant productivity and distribution (Fisher and Turner, 1978). However, depending on their level of resistance, many plant species can successfully cope with varying degrees of drought by modifying their morphological, physiological and metabolic processes (Clark and Durley, 1981; Hanson and Hitz, 1982). It is believed that the altered phenotype of plants with an enhanced ability to survive and grow under environmental stresses is largely the result of changes in gene expression (Sachs and Ho, 1986). Indeed, It has been well documented that plant adaptive responses to water stress are accompanied by the accumulation of specific mRNAs (Bray, 1988; Chen and Tabaeizadeh, 1992a,b). The changes in gene expression can also be partly induced by application of exogenous abscisic acid (Bray, 1988; Chen and Tabaeizadeh, 1992a,b), the plant hormone which appears to modulate the response of plants to water-stress (Skriver and Mundy, 1990). During the last few years, a number of drought- and ABA-responsive genes have been isolated and characterized from several species (Baker et al., 1988; Mundy and Chua, 1988; Gomez et al., 1988; Skriver and Mundy, 1990; Chen et al., 1993). These gene products may protect cells from damage at low water potentials (Baker et al., 1988).